There is an IR transmitter and receiver located just above the wheel. The signals are transmitted to the wheel and when the white portion is in the proper position the IR receiver reacts to the signal. When the black portion is in the proper position the beam stops being transmitted.

This whole effort is utilized to report to the Micro Controller that the Roomba is moving and not stuck somewhere. If the stasis reports are inhibited by removing the IR signals for any amount of time then the Roomba will stop running and report an error condition.

Hi R.D.O. I looked at your tutorial and think you did quite a nice job of preparing its graphics and story-line.

Regarding the caster-wheel replacement, you were very fortunate to find mass produced hardware of exactly the correct diameter and thickness!

Regarding the use of the flat-washers, I presume them to be made of steel, and of course the wheel-axle is also a steel composition (but likely not identical to that of the washers). In your design, the washer-holes are serving as axle-bearings, and I think the combination of steel (washers) rubbing on the steel-shaft, in combination with the small thickness of each washer will become a wear problem for you.

Roomba presents quite a large load on that caster-wheel, since more than half the battery's weight is bearing down on that wheel! You may notice some audible squeaking sounds, and notice the washer holes enlarging, or grooves forming in the axle.

Some lubrication would help control wear, but the chosen lubricant would have to be compatible with the "stamp" material!

Regarding the caster-wheel replacement, you were very fortunate to find mass produced hardware of exactly the correct diameter and thickness!

heu.... YES !!!!!♦The first thing that I try to resolve my problem was so easy to do because all things were so "adaped" that I thank that I must tell that to other people !!!!!!

Regarding the use of the flat-washers, I presume them to be made of steel, and of course the wheel-axle is also a steel composition (but likely not identical to that of the washers). In your design, the washer-holes are serving as axle-bearings, and I think the combination of steel (washers) rubbing on the steel-shaft, in combination with the small thickness of each washer will become a wear problem for you.

I don't know, because the whashers are used at the left and right, for the rubber wheel don't touch the hard plastic case at left and right and grip on it. But the washers turns withs the steel-axe. The system [axe+rubber stamps+ washers] is rotating.
I say in my tuto that i' was lucky that the axe rotate on the case. But I think that it's the original wheel who is suppose to turn on the axe, and you raise an interesting problem : How the hard plastic case will be worn by the rotation of the axe ?
I will tell you that in few years !!!